Hitherto, there has been known a method for producing silica sol through neutralization or ion-exchange of water glass serving as a raw material. Also, it has been known that silica micropowder is produced through pyrolysis of silicon tetrachloride. A known method for producing a high-purity silica sol is based on hydrolysis of an alkoxysilane in an alcoholic aqueous solution in the presence of a basic catalyst. In one reported method, a 0.28 mol/L tetraethyl silicate is added to an alcoholic solution containing several mol/L-order ammonia and several mol/L to 15 mol/L water, and the mixture is hydrolyzed, to thereby obtain silica particles having a diameter of 50 to 900 nm (see, for example, Non-Patent Document 1).
In one proposed method for producing a dispersion of silica particles, an untreated silica material having a Q4/Q3 value of 0.5 to 5.0 is subjected to a hydrothermal treatment, wherein Q3 is a peak signal area in an 29Si-NMR spectrum observed in a chemical shift of −94 ppm to −103 ppm, and Q4 is a peak signal area in a 29Si-NMR spectrum observed in a chemical shift of −103 ppm to −115 ppm (see, for example, Patent Document 1). The untreated silica material employed in the Examples of Patent Document 1 has a dispersion particle size (a median size as determined through a dynamic light scattering method) of 58 nm and a mean particle size as determined through TEM observation of 44 nm.
In one proposed method for producing silica hollow particles, silicic acid or a silicate salt is hydrolyzed to condensate in the presence of a basic catalyst, to thereby form a silica coating layer on core particles such as calcium carbonate particles, and the silica coating layer is subjected to a hydrothermal treatment (see, for example, Patent Document 2).
There has been proposed a method for producing a silica sol for use as an abrasive, wherein a raw material is subjected to a hydrothermal treatment in the presence of an alkaline species such as NaOH, KOH, or a quaternary ammonium (see, for example, Patent Document 3).